1. Field of the Invention
The present invention generally relates to rotary vane pumping machines, and more particularly, to an apparatus providing for rotary-linear vane guidance in a rotary vane pumping machine.
2. Description of the Related Art
The overall invention relates to a large class of devices comprising all rotary-vane (or sliding vane) pumps, compressors, engines, vacuum-pumps, blowers, and internal combustion engines.
This class of devices includes designs having a rotor with slots with a radial component of alignment with respect to the rotor's axis of rotation, vanes which reciprocate within these slots, and a chamber contour within which the vane tips trace their path as they rotate and reciprocate within their rotor slots. The reciprocating vanes thus extend and retract synchronously with the relative rotation of the rotor and the shape of the chamber surface in such a way as to create cascading cells of compression and/or expansion, thereby providing the essential components of a pumping machine. Some means of radially guiding the vanes must therefore be provided to ensure contact, or close proximity, between the vane tips and chamber surface as the rotor and vanes rotate with respect to the chamber surface.
With conventional designs, this radial guidance of the vanes has been provided by a number of means which necessitate undesirable high-speed frictional motion. One common means of guidance utilizes the tips of the vanes as a sliding frictional interface against the chamber contour. With this means employed, inertial and/or fluid forces push the vanes against the chamber surface to provide adequate sealing. Another means utilizes a pin at one or both ends of the vanes, each pin riding within a channel or against a cam to provide guidance of the vanes. Floating followers may be employed around the pins to provide a hydrodynamic wedge against the cam surface. Alternatively, the device may be configured such that one or more sleeve or cam follower bearings are employed around each pin to provide a rolling interface against the cam.
These conventional means of guiding the vanes all suffer from a common shortcoming, namely that high linear speeds are encountered at the radial-guidance frictional interface. These high speeds severely limit the maximum speed of operation and thus the maximum flow per given engine size. Furthermore, the maximum inertial and/or fluid-pressure forces which can be resisted by the frictional interface is limited. In the case of a hydrodynamic interface, the high heat-flux and shearing rate involved limit the maximum force and speed and the viscosity of lubricant which can be employed. The hydrodynamic interface also limits the precision of the radial vane guidance that may be obtained, as sufficient clearance must be provided for the hydrodynamic oil film. In the case of the cam follower bearings, the maximum size of the cam follower is limited by many factors including the size of the device, the speed of rotation, and the angular acceleration torques produced as the radial position of the vanes change throughout their cycle of rotation. The cam follower size limitation limits the maximum force the followers can resist. The high speeds involved combined with the high angular acceleration torques on the cam followers can produce significant power losses, heat buildup, and/or wear. These above limitations severely reduce the potential effectiveness of the vane device.
However, several advantages are evident in the sliding-vane geometry as in the present invention. One such advantage is that cascading cells of compression and/or expansion are created as the vanes sweep by the chamber surfaces, thereby forming multi-stage sealing which improves sealing efficiency.
Another advantage of this basic geometry is that the chamber surface is significantly steady-state with respect to temperature and pressure, provided sufficient vane stages are employed. In other words, the region of the cycle, temperatures, and pressures "seen" by the chamber surface at a given location do not change significantly as the vanes sweep by. This characteristic contrasts with the significantly non-steady-state quality of a cylinder wall of a piston pumping machine, wherein locations on the cylinder wall experience drastic changes in pressure and temperature throughout the cycle. Because of this steady-state component within the chamber surfaces of this sliding-vane geometry, specific regions of the cycle can be targeted or accessed simply by selecting a site on the chamber surface. For instance, a combustion residence chamber within an internal combustion engine embodiment can be employed to enhance lean combustion characteristics as described in U.S. Pat. No. 5,524,586 to Mallen and U.S. Pat. No. 5,524,587 to Mallen et al.
This steady-state component and sweeping vane arrangement has certain advantages compared with a piston engine or orbital designs, such as those shown in U.S. Pat. Nos. 4,021,160; 4,037,997; 4,079,083; and Re. 29,230.
One advantage is the ability to place large, continuously-open intake and exhaust scavenging ports in the engine, such ports not requiring complex valves or valve trains for their timing. Another is that this steady-state component can also serve to boost thermal efficiency by reducing the chamber wall heat-flux from the hotter regions of the cycle.
The steady-state component of the chamber surfaces thus offers many potential advantages to designers of engines or pumping machines by virtue of the ability to easily and efficiently access different parts of the device's cycle without requiring valves or other complex means to do so.
In light of the foregoing, there exists a need for a sliding-vane pumping geometry, wherein multiple vanes sweep in relative motion against the chamber surfaces, which incorporates a radial-guidance frictional interface operating at a reduced speed compared with the tangential speed of the vanes at the radial location of the interface. This interface should furthermore permit higher loads at high rotor rotational speeds to be sustained by the bearing surfaces than with conventional designs. With such an improved design, much higher flow rates could be achieved within a given size pumping device or internal combustion engine, thereby improving the performance and usefulness of these machines.